Drilling fluids are used while drilling bore holes in subterranean formations. Oil-based drilling fluids are used for recovering oil as well as gas. However, commercially available drilling fluids have limited thermal stability and are known to exhibit a decrease in fluid loss control after being exposed to high temperatures.
Wellbore service fluids including maleic anhydride grafted alpha-olefin homopolymer combined with neat poly(styrene-b-ethylene/butylene-b-styrene) (SEBS) block copolymers have been used in oilfield applications to address this problem.
The present invention addresses this by using a grafted SEBS block copolymer to obtain fluid loss control instead of the combination of grafted homopolymer and SEBS. SEBS has better soluability than alpha-olefin homopolymer in oil and it has a high temperature stability attributes due to the lack of an unstable double bond.